Not Applicable
Not Applicable
Not Applicable
1. Field of the Invention
The present invention relates to a cardiac assist device and more particularly to an implantable artificial left ventricle including a continuously operating pump and hydraulic valve system which assists the heart by intermittently pumping blood in synchronization with operation of the heart.
Congestive heart failure represents an enormous national public health concern, with,a prevalence of 4.9 million cases and an incidence of more than 400,000 cases a year. Some 50,000 people a year die of heart failure and it is a contributing factor in 250,000 additional deaths a year.
Congestive heart failure accounts for more than 800,000 hospitalizations a year, at a hospital cost of $18.8 billion. The direct and indirect cost of treating this disease has been estimated at $64 billion a year.
Congestive heart failure is the only form of heart disease that is increasing in the United States. It will undoubtedly continue to do so, as more and more victims of coronary occlusions survive and their longevity is increased. However, with each such event, the heart muscle is further injured and the resulting scar tissue decreases the ability of the left ventricle to perfuse the body. Thus, higher survival rates and increased longevity lead to an increased number of people surviving long enough for congestive heart failure to become a likelihood. The development of a device to augment or replace the pumping ability of the left ventricle would prevent congestive heart failure.
(2) Description of Related Art Including Information Disclosed Under 37 CFR 1.97 and 1.98
During the last twenty years, a variety of mechanical devices have been developed to support circulation. These devices, known as ventricular assist devices, usually aimed at the left ventricle, (sometimes known as LVAD""s) have been used primarily for temporary short-term-circulatory support as a bridge to cardiac transplantation. The success of these devices has led to the understanding that LVAD""s may well be developed as a long-term therapy for patients with end-stage heart disease. Further, the utilization of LVAD""s for patients with chronic heart disease has been recognized as a permanent treatment option for many patients.
The existing implantable cardiac assist ventricles either modify the anatomy of the heart (apico-aortic assist), replace the heart entirely, or use an atrial to aortic pump which provides a constant blood flow.
The present invention takes a different approach. It is essentially an implantable artificial ventricle that leaves the heart intact, improves the function and nutrition of the cardiac muscle, and normalizes the perfusion of the entire vascular system. Our device is designed such that in the event of mechanical failure, it will not impede pre-implantation operation of the heart. Hence, the patient is not medically worse off than he would have been without the device, if it were to fail.
The present invention utilizes a counterpulsation pumping action and a unique valve structure. The device pumps blood during each cardiac diastole but not during cardiac systole. The result is that the work of the heart is decreased during systole. Coronary blood flow and perfusion of the heart itself are increased during cardiac diastole, when the transmural cardiac resistance is at its nadir. The increased coronary flow during cardiac diastole has an angiogenic effect, i.e., it promotes the formation of new coronary collateral channels. This beneficial effect has been shown to be associated with an improvement in left ventricular function, and a significant decrease in angina.
Our invention provides for long term implantation of a counterpulsating chamber in the descending aorta, either above the diaphragm or below the inferior mesenteric artery, which will assist the failing or failed left ventricle. Candidates for such an assist system would, at first, be NYHA Grade IV patients, in chronic failure and bedridden. As the procedure gains acceptance, it would be implanted in somewhat less severely ill patients.
We utilize a closed hydraulic fluid system which includes a hydraulic pump. The pump has a continuously operating voice coil linear electric motor which drives a hydraulic piston. The motor and piston are preferably constructed as a single sealed unit, with the motor submersed in hydraulic oil, so as to be supported on its own hydrodynamic oil bearing. Such a pump is disclosed in detail in U.S. Pat. No. 5,360,445, entitled xe2x80x9cBlood Pump Actuator,xe2x80x9d issued to Goldowsky on Nov. 1, 1994.
As indicated in the Goldowsky patent, this arrangement greatly increases the life of the pump by eliminating wear at the bearings. The hydraulic fluid is selected to have a very low viscosity and very good lubrication capability.
Hydraulic valves are utilized to convert the continuous fluid flow output of the pump into the intermittent fluid flow needed to provide the desired counterpulsed blood flow. The valves are controlled in accordance with electrical signals from the heart such that blood is pumped only during cardiac diastole.
The valves are situated in a multi-valve body or chamber. After closure of the aortic valve, hydraulic fluid is pumped into a variable volume chamber which expands, causing blood to be forced into the arteries. During the next cardiac systole, fluid is pumped from the chamber, into a fluid reservoir which accumulates the fluid during pump diastole, such that no force is exerted by the device on the circulatory system.
A bypass is employed to relieve the fluid build-up in the chamber, if the pressure rises above a given level. This might take place, for instance, if a pause occurs in the operation of the valves due to a pause in the rhythm of the heart. The bypass permits the pump to continue to operate without overloading the closed hydraulic system.
It is therefore a prime object of the present invention to provide an implantable cardiac assist device which operates in a counterpulsation mode.
It is therefore another object of the present invention to provide an implantable counterpulsation cardiac assist device which utilizes a continuously operating hydraulic pump in a closed hydraulic system.
It is still another object of the present invention to provide an implantable counterpulsation cardiac assist device with hydraulic valves regulated in accordance with heart operation.
It is still another object of the present invention to provide an implantable counterpulsation cardiac assist device which includes a tubular element adapted to be implanted in the aorta and having a variable volume hydraulic chamber.
It is still another object of the present invention to provide an implantable counterpulsation cardiac assist device where the caudad end of the tubular element includes a unidirectional pressure sensitive valve.
It is still another object of the present invention to provide an implantable counterpulsation cardiac assist device which increases coronary blood flow.
It is still another object of the present invention to provide an implantable counterpulsation cardiac assist device which promotes the formation of new coronary collateral channels.
It is still another object of the present invention to provide an implantable counterpulsation cardiac assist device which promotes perfusion of the heart.
It is still another object of the present invention to provide an implantable counterpulsation cardiac assist device which, in the event of mechanical failure, does not impede the operation of the heart.
In accordance with one aspect of the present invention, an implantable cardiac assist device is provided, adapted to be inserted in an artery. The interior of the device is divided into first and second variable volume chambers. The first chamber is connected to the artery. A continuously operating pump is hydraulically connected to the second chamber by valves means which regulate fluid flow to the second chamber in response to the operation of the heart, for directing fluid flow to the second chamber during cardiac diastole and away from the second chamber during cardiac systole.
The device includes a generally tubular element. A unidirectional pressure sensitive blood flow valve is situated proximate one end of the tubular element.
The device also includes a rigid shell. The shell is attached to tubular element, over an opening in the element wall. A flexible diaphragm is situated within the shell and divides the interior into separate chambers.
Control means for the valve means are provided. The control means includes means for monitoring the operation of the heart and for actuating the valves to regulate fluid flow to the second chamber in accordance with same. Monitoring means may be an electrocardiograph and, if present, a cardiac pacemaker as well.
The pump has a fluid inlet and a fluid outlet which are connected to a closed hydraulic system. The system includes a fluid reservoir to retain hydraulic fluid. The valves connect the pump outlet to the reservoir during cardiac systole. The valves connect the pump inlet to the second chamber during cardiac systole.
The system further includes a bypass conduit for connecting the pump output and the pump input. A bypass valve is situated in the bypass conduit.
The artery into which the element is inserted is preferably the descending aorta. The element is placed in the descending aorta between the coronary arteries and heart, on the one hand, and the femoral and Iliac arteries, on the other hand.
An electric motor forms a part of the pump. transcutaneous energy transmitter is utilized to provide energy to the motor.
An electrocardiograph is provided for monitoring the operation of the heart. Means are provided for connecting the electrocardiograph to the valve control means.
In accordance with another aspect of the present invention, an implantable cardiac assist device is provided comprising a tubular element adapted to be situated in the descending aorta. A unidirectional pressure sensitive valve is situated in the end of the element facing away from the heart. First and second variable volume chambers are provided within a shell which is associated with the element. The first chamber is connected to the artery. A continuously operating pump, having an inlet and an outlet, is connected to a closed hydraulic system, including a fluid reservoir. Valve means, responsive to the operation of the heart, are provided for connecting the pump outlet to the second chamber, and the reservoir to the pump inlet, when the heart is in diastole. The valve means connects the pump outlet to the reservoir, and the second chamber to the pump inlet, when the heart is in systole. Bypass means are provided for connecting the pump outlet and the pump inlet.
The operation of the pressure sensitive valve is preferably synchronized with the valve means. In one embodiment, an electrically activated valve is utilized and is controlled by the valve means controller. In a second embodiment, a hydraulically actuated valve is utilized. In the latter case, the valve control input is connected by a conduit to the second chamber.